The present invention relates to a semiconductor single crystal growing technology using Czochralski method, and more particularly to a semiconductor single crystal growing apparatus and growing method in which crystal growth is performed while a magnetic field and a current orthogonal to each other are applied to a semiconductor melt to rotate the semiconductor melt.
Semiconductor crystal wafers in use for the substrates of ultra high integrated electric devices are grown by Czochralski method in which a semiconductor single crystal is pulled up from a rotating semiconductor melt while it is rotated in the opposite direction. The semiconductor melt held in the crucible undergoes heat from a cylindrical heater installed around the crucible. The crucible is rotated so that the temperature distribution in the melt shows perfect axial symmetry about the pull axis of the crystal. Rendering the temperature distribution in the melt axially symmetrical requires that the center of rotation of the crucible and the symmetric axis of the heater arrangement coincide with the pull axis of the crystal. The conventional art typically employs a method of mechanically rotating a shaft that holds the crucible.
This crucible rotation changes the concentration of the impurities involved in the crystal. In the method of mechanically rotating the crystal and the crucible, however, the crystal rotation has become difficult with increasing crystal diameter; besides, rotating a crucible requires a system of considerable size. For such reasons, the growth of large crystals has become increasingly difficult.
In order to circumvent this difficulty, there has been proposed a semiconductor crystal growing apparatus and growing method comprising a device for applying a magnetic field to a semiconductor melt under crystal growth and a device for applying a current orthogonal to the above-mentioned magnetic field to the semiconductor melt, and wherein an electrode to be immersed into the semiconductor melt and an electrode for energizing the pulled crystal are used (Japanese Patent Application No.Hei 9-343261). This technology minimizes the increase in apparatus scale and allows precise control of the rotation rate even when a semiconductor crystal with a diameter as large as 30 cm or more is grown. In addition, Japanese Patent Application No.Hei 10-065174 has shown that the electrode material is made identical to the semiconductor single crystal to grow so that contamination to the growing crystal is avoided.
In the conventional art described above, however, the electrode was dissolved into the semiconductor melt over the course of crystal growth. In order to keep applying the current, the electrode needed to be moved with the crystal growth. Besides, when the electrode was put into contact with the semiconductor melt, the melt directly below the electrode was pulled up so that the contact was made at a position higher than the melt surface. Accordingly, there was another problem that the surface form of the melt between the electrode and the growing crystal changes to cause a drop in rotation symmetry.
Moreover, it was impossible in the above-mentioned conventional semiconductor single crystal growing technologies to monitor the rotation rate of the semiconductor melt under crystal growth with a high degree of accuracy and with facility.
Furthermore, in such methods as the conventional ones, of applying a magnetic field and a current of constant intensities to rotate the semiconductor melt, it was difficult to render a single piece of crystal uniform in the impurity distribution along the direction of growth, with variations of not greater than 1%. In particular, in the cases of silicon single crystals, it was difficult to distribute both oxygen and a dopant impurity uniformly at the same time. Thus, in the conventional methods, it was difficult to control the impurity concentrations in a crystal along the crystal pulling direction, and it was difficult to improve uniformity in the impurity distribution within a semiconductor single crystal along the direction of growth.
The present invention has been achieved in view of the foregoing problems. An object thereof (hereinafter, may be referred to as first object) is to provide a semiconductor single crystal growing technology using Czochralski method. comprising a semiconductor single crystal growing apparatus and growing method for applying a magnetic field to a semiconductor melt under crystal growth and passing a current orthogonal to the magnetic field through the semiconductor melt, and wherein an electrode need not be moved due to electrode dissolution during crystal growth, and any drop will not occur in the rotation symmetry of the semiconductor melt due to a deformation in the melt surface between the electrode and the growing crystal.
Moreover, another object of the present invention (hereinafter, may be referred to as second object) is to provide an apparatus and method which make it possible in the conventional crystal growing to accurately and easily monitor the rotation rate of a semiconductor melt that rotates under electromagnetic forces during crystal growth.
Furthermore, another object of the present invention (hereinafter, may be referred to as third object) is to provide an apparatus and method which make it possible in the conventional crystal growing to improve the uniformity in the impurity distribution within a semiconductor single crystal along the direction of crystal growth.
In order to achieve the first object described above, the present inventors have made thorough intensive study and found that the above-mentioned object can be achieved by the provision of a semiconductor crystal growing apparatus comprising a device for applying a magnetic field to inside a semiconductor melt and a device for passing a current through the semiconductor melt, wherein: a protective tube is arranged around an electrode for passing the current through the semiconductor melt; the material of the protective tube is made identical to that of a crucible holding the semiconductor melt; the protective tube and the melt are put into rectangular contact with each other; and the semiconductor melt and the electrode for passing the current through the semiconductor melt are put into contact with each other in the interior of the protective tube, at a position higher than the major surface of the melt surface, so that the semiconductor melt and the electrode for passing the current through the semiconductor melt are always in contact with each other during crystal growth and there occurs no deformation in the melt surface between the electrode and the crystal. Thereby has been achieved the present invention (hereinafter, may be referred to as first invention).
Thus, the first invention provides a semiconductor crystal growing apparatus comprising a device for applying a magnetic field to inside a semiconductor melt and a device for passing a current through the semiconductor melt, characterized in that an electrode for applying the current to inside the semiconductor melt extends through a tube surrounding the electrode.
The first invention also provides a semiconductor crystal growing method for growing a semiconductor crystal by using a semiconductor crystal growing apparatus comprising a device for applying a magnetic field to inside a semiconductor melt and a device for passing a current through the semiconductor melt, the method being characterized in that the semiconductor crystal growing apparatus has an electrode for applying the current to inside the semiconductor melt, the electrode extending through a tube surrounding the electrode.
In the first invention, a current is passed between the semiconductor melt held in a magnetic field and the growing semiconductor crystal, with the protective tube arranged around the electrode; therefore. the electrode and the melt come into contact with each other in the interior of the protective tube. Thus, even when the contact portion between the electrode and the melt increases in temperature during crystal growth, the melt rises inside the electrode, precluding the electrode and the melt from getting out of contact with each other. As a result, it becomes possible to keep applying the current without moving the electrode during crystal growth. Moreover, the material of the protective tube arranged around the electrode is made identical to that of the crucible holding the semiconductor melt so that the protective tube and the semiconductor melt come into rectangular contact with each other so as not to pull up the melt directly below the electrode. Therefore, the melt surface between the electrode and the growing crystal is not deformed any longer. This enhances the axial symmetry in temperature distribution, thereby making it possible to further uniformize the radial distribution of the dopant impurity concentration involved in the crystal. Furthermore, in the cases of silicon single crystals, the oxygen concentration distribution can also be rendered more uniform in radial distribution.
The present invention to achieve the foregoing second object (hereinafter, may be referred to as second invention) provides a semiconductor single crystal growing apparatus for performing semiconductor single crystal growth by Czoohralski method, comprising a device for applying a magnetic field to inside a semiconductor melt and a device for passing a current orthogonal to the magnetic field through the semiconductor melt, characterized in that a float for rotating with the melt is arranged on the surface of the semiconductor melt.
The second invention also provides a semiconductor single crystal growing method for performing semiconductor single crystal growth by Czochralskl method, characterized by using a semiconductor single crystal growing apparatus having a device for applying a magnetic field to inside a semiconductor melt and a device for passing a current orthogonal to the magnetic field through the semiconductor melt, a float for rotating with the melt being arranged on the surface of the semiconductor melt, and in that the movement of the float for rotating with the melt is detected to monitor the state of rotation of the semiconductor melt with the movement.
In the second invention, while a current is applied to between the semiconductor melt held in a magnetic field and the growing semiconductor single crystal and the semiconductor melt is rotated by electromagnetic forces for crystal growth. the rotation rate of the semiconductor melt can be monitored by virtue of the float that is floated on the melt surface. This makes it possible to obtain impurity concentrations in accordance with the rotation rates, as well as achieve a change in concentration in the middle of crystal growth.
In this case, the semiconductor single crystal growing apparatus may also suitably adopt the following configurations:
(A) A configuration in which the above-mentioned float has the shape of a ring.
(B) A configuration in which the above-mentioned ring-shaped float is arranged so that the growing crystal grows inside of the ring of the float.
(C) A configuration in which the material of the above-mentioned float is the same as that of a crucible holding the semiconductor melt.
(D) A configuration In which the above-mentioned ring-shaped float is provided with a deformed portion at the ring.
(E) A configuration in which the above-mentioned deformed portion is arranged on the outer periphery of the ring.
(F) A configuration in which the above-mentioned deformed portion is arranged on the top surface of the ring.
(G) A configuration in which the above-mentioned deformed portion is protruded from the ring.
(H) A configuration in which the above-mentioned deformed portion is a recess in the ring.
(J) A configuration in which the above-mentioned deformed portion is a hole piercing through the ring.
The present invention to achieve the foregoing third object (hereinafter, may be referred to as third invention) provides a semiconductor crystal growing apparatus using Czochralski method, comprising a device for applying a magnetic field and a current orthogonal to each other to inside a semiconductor melt, characterized by the provision of a magnetic field control unit for changing the magnetic field during crystal pulling and/or a current control unit for changing the current during crystal pulling.
The third invention also provides a semiconductor crystal growing method using Czochralski method, for applying a magnetic field and a current orthogonal to each other to inside a semiconductor melt, characterized in that the magnetic field applied and/or the current applied are/is changed during crystal growth.
In the third invention, while a current Is applied to between the semiconductor melt held in a magnetic field and the growing semiconductor single crystal and the semiconductor melt is rotated by electromagnetic forces for crystal growth, the intensity of the magnetic field and the value of the current to be applied is changed with the time of crystal growth so that the rotation rate of the melt can change with the crystal growth time, i.e. the pull length of the crystal, to offer an impurity concentration according to the rotation rate. Obtaining the relation between the rotation rate and the impurity concentration in advance makes it possible for variations in the impurity concentration resulting from segregation during the crystal growth to be compensated with variations of the rotation rate, so that the semiconductor single crystal is uniformized in impurity concentration distribution over the direction of growth.
In the third invention, the magnetic field applied and/or the current applied are/is suitably changed during the crystal growth in accordance with a crystal pull length or a crystal pull time. Moreover, a magnetic field signal parameter to change is appropriately the strength of the magnetic field, and a current signal parameter to change is the value of the current.